Keratinocyte Arginase1 regulates pro-inflammatory responses and drives re-epithelialisation via Lipocalin2.

Background and objectives: Chronic skin wounds exhibit impaired re-epithelialisation due to defective keratinocyte migration and increased susceptibility to infection. Arginase1 (ARG1) is an enzyme expressed by keratinocytes that has been shown to be important for skin wound healing.
However, the mechanisms underpinning keratinocyte ARG1 function in wound closure are not fully understood. Here, we investigate the role of ARG1 in keratinocyte wound closure and its potential for contributing to anti-microbial defence.

Methods: In vitro 2D wounding assays using ARG1 inhibited keratinocytes were used to explore the function of ARG1 in keratinocyte scratch closure. ARG1 was also assessed in human clinical skin wounds.

Results: ARG1 was strongly expressed in the perilesional regions of acute wounds but its expression was dysregulated in chronic ulcers, with high expression in the upper layers of the hyperplastic epidermis. ARG1 inhibition in keratinocytes led to a significant decrease in 2D scratch closure, augmented Interleukin 1 (IL-1) family- and Tumour Necrosis Factor α (TNF α- driven pro-inflammatory
signalling, and significantly downregulated the Anti-microbial Peptide (AMP) Lipocalin 2 (LCN2). In response to infection challenge, LCN2 expression was lower in ARG1 deficient cells. LCN2 neutralisation in keratinocytes delayed scratch wound closure. The metabolic products downstream of ARG1 activity, putrescine (Put) and urea, rescued keratinocyte migration and LCN2 expression in ARG1 deficient cells.

Conclusions: ARG1 plays a major role in keratinocyte re-epithelialisation, regulating inflammation and LCN2 production in sterile and infected wound conditions. In culture, impaired wound responses of ARG1-inhibited cells can be rescued by ARG1 downstream products Put and urea, highlighting the complexity of ARG1 control of wound healing. Manipulation of the ARG1 pathway may have the potential to be used for the management of skin wounds. ARG1 has been previously reported to be dysregulated in chronic lesions, expression patterns being dependent upon the type of wound analysed. Further study of the pathway is needed to fully understand the role of ARG1 in chronic wounds.